Field of the Invention
Embodiments of the present invention relate generally to a charged particle beam writing apparatus and a charged particle beam writing method, and more specifically, relate to a writing apparatus and method that estimate a deflection time, being a part of writing time, for performing beam deflection between subfields (SFs), for example.
Description of Related Art
In recent years, with high integration of LSI, the line width (critical dimension) of circuits of semiconductor devices is becoming progressively narrower. As a method for forming an exposure mask (also called a reticle) used to form circuit patterns on these semiconductor devices, the electron beam (EB) writing technique having excellent resolution is employed.
FIG. 14 is a conceptual diagram explaining operations of a variable-shaped electron beam writing or “drawing” apparatus. The variable-shaped electron beam writing apparatus operates as described below. A first aperture plate 410 has a quadrangular aperture 411 for shaping an electron beam 330. A second aperture plate 420 has a variable shape aperture 421 for shaping the electron beam 330 having passed through the aperture 411 of the first aperture plate 410 into a desired quadrangular shape. The electron beam 330 emitted from a charged particle source 430 and having passed through the aperture 411 is deflected by a deflector to pass through a part of the variable shape aperture 421 of the second aperture plate 420, and thereby to irradiate a target object or “sample” 340 placed on a stage which continuously moves in one predetermined direction (e.g., x direction) during writing. In other words, a quadrangular shape that can pass through both the aperture 411 of the first aperture plate 410 and the variable shape aperture 421 of the second aperture plate 420 is used for pattern writing in a writing region of the target object 340 on the stage continuously moving in the x direction. This method of forming a given shape by letting beams pass through both the aperture 411 of the first aperture plate 410 and the variable shape aperture 421 of the second aperture plate 420 is referred to as a variable shaped beam (VSB) system.
In the writing apparatus, when writing a chip pattern, the time for writing the chip pattern is estimated and the estimated time is provided to the user (e.g., refer to Japanese Patent Application Laid-open (JP-A) No. 2009-088213). Further, in the writing apparatus, a multi-stage deflection system is employed to write a pattern at a desired position. According to the multi-state deflection system, the writing region of a target object is divided into a plurality of small regions called subfields (SFs), a beam position is deflected to an SF by one deflector of multiple stage deflector, and the beam position is deflected to a pattern forming position in the SF concerned by another deflector, thereby writing a pattern at a desired position. Therefore, in addition to the time for a pattern to be written in each SF, the time for the beam to travel (move) between SFs should be considered in the writing time. Conventionally, the traveling time of the beam is calculated based on a value obtained by multiplying a divided value, which is calculated by dividing an x-direction chip size by the SF size, by a divided value, which is calculated by dividing a y-direction chip size by the SF size. That is, the traveling time of the beam is calculated on the assumption that the beam moves between all the SFs in a chip. However, patterns are not necessarily arranged in all the SFs that correspond to the chip region. In a VSB system, it is possible to skip an SF where no pattern exists and move to another SF. Conventionally, the traveling time to a skipped SF has been included in the writing time. Therefore, there is a problem in that the error of the estimated writing time has been increased. Thus, in order to highly accurately calculate the time required for a beam to move between SFs, it is important to distinguish an SF where a pattern exists from an SF where no pattern exists, and to count the number of SFs where patterns exist. However, conventionally, such a method of counting the number of SFs where patterns are arranged has not been established. Therefore, there is a problem in that the difference between the estimated writing time and the actual writing time has been increased.